The present invention relates to air conditioners, air cleaners, air curtains, employing a cross-flow fan as a blowing mechanism and, more particularly, to a blowing mechanism with a low noise level even when a clogged filter increases a flow resistance on an air suction side.
In air conditioning equipment plants employing cross-flow fans, to suppress the increase of noise attributable to a back flow which develops when the flow resistance of the air has increased due to a clogged filter, in, for example, Japanese Patent Publication 21162/1975, a back flow preventing mechanism locally extends from each side end face of the cross flow fan to a central part thereof in a discharge space.
Additionally, in Japanese Patent Laid-Open 5903/1975 and 115408/1977, an apparatus is provided which is furnished with guide vanes forcibly deflecting the streams of air from a heat exchanger to a cylindrical bladed rotor of the cross-flow fan in a suction side space to thereby increase the flow rate of the air.
It is desirable to reduce the noise level in air conditioning equipment and plants; however, in air conditioning equipment and plants employing a cross-flow fan, vortices, peculiar to the cross-flow fan exist, so that a discharge passage has, in effect, a cross sectional area thereof reduced thereby resulting in the problem that the flow velocity of air passing through the vanes to the cross-flow fan in the discharge section raises the level of noise generated.
A method for solving this problem is such that the spread angle of a casing which is formed into a helical shape is widened so as to expand the discharge passage and to lower the flow velocity, whereby the noise level is lowered. In the case of adopting the spread casing, however, the position of the vortex near a side plate at each end face of the cylindrical bladed rotor of the cross-flow fan becomes very unstable, and the backflow is liable to develop, particularly when the fluid resistance has increased due to, for example, the adhesion of dust to the filter disposed on the air suction side or the installation of an air cleaning filter. When the backflow has developed at one end face of the cylindrical bladed, another backflow develops also at the other end face with a difference in time. A cyclic backflow phenomenon in which the developments of the backflow recur, arises continuously. The resulting unsteady sound raise the problem that, when the fluid resistance of the suction passage has increased, any of the silent air-conditioning equipment and plants cannot be provided.
With the apparatus proposed in the aforementioned Japanese Patent Publication No. 21162/1975 problems arise in that, when the spread angle of the casing is widened, the backflow preventive effect of the apparatus is lost, so the unsteady sound develops, and, since the discharge passage has its cross-sectional area reduced, the specific characteristic of the cross-flow fan is sacrificed, and the rotational speed of the fan is inevitably increased for increasing the flow rate, so the level of noise rises.
The apparatus disclosed in the aforementioned Japanese Patent Laid-Open No. 5908/1975 or No. 115408/1977 is such that the guide vane is mounted in the suction side space, and that the air streams from the heat exchanger to the cylindrical bladed rotor of the cross-flow fan are forcibly deflected by the vane, to thereby increase the flow rate. However, the forcible deflection, results in the problems of the streams becoming turbulent behind the guide vane flow into the fan blades, so a turbulent flow noise increases, and blade passing noise also increases. Thus, it has been impossible to provide an apparatus with a means for effectively reducing a level noise generated.